1. Field of the Invention
The invention relates to a serial charger with the function of automatic change of charging speed for NiCd/NiH batteries, and more particularly to a charger with a speedy charging process that can be realized even on low power condition by use of the automatic speed changing principle. Accordingly, an exchange power unit can be reduced in size and built in the charger so that the charger is convenient to carry and the finished charging time can be adjusted automatically according to the demand of battery consumption of customers.
2. Description of the Related Art
With the increasing population of 3C portable electronic products, the demand on batteries increase proportionally. Because the normal unrechargeable batteries will be discarded after use, the operation cost will thus increase and it will also lead to the pollution of environment. Therefore, compared with the normal battery, the rechargeable battery (or so-called secondary battery) can reduce the cost and avoid pollution stemming from the battery. The quantity of rechargeable battery increased steadily and the demand on charging devices rises accordingly. But the normal charger for NiCd or NiH batteries employs either parallel charging principle or serial charging principle. For the parallel charging charger, the electronic control devices are difficult to select and couple, the requirements of instant charging process can not be met and it has defects.
The serial charging charger recharges several batteries in series with constant current and voltage. With the development of electronic technique, the charging type has evolved from the slow charging (more than 8 hours) in the beginning step to instant charging, which will also take four to five hours. Recently, the charger was developed with speedy charging or so-called super speedy charging process.
FIGS. 1 and 2 show a disassembled and an assembled diagram of a conventional instant charging device. Because it charges four serial batteries with constant current and voltage, the charging time of four batteries is identical, that is, it takes always four hours to charge four batteries or one battery. The user cannot adjust the charging time according to the number of batteries by himself. For the customers who urgently need batteries, this charging process is too slow. But this kind of instant charger 10 do have some advantages. Since its charging speed is not extreme, the needed power is not much. The exchange power unit 12 can be installed in the circuit board, and the plug 14, which connects to the AC current outside, can also be positioned under the housing 15. Because no outer transformer is needed, the whole size is thus fairly little and it is easy to carry and use.
A speedy charging device is an innovation aiming to further reduce the long charging time of the instant charger 10. It provides a big but constant current over the charging process of the secondary battery. We know that the current I and the time T are the significant factors for electric charge. That is to say, the battery electric capacity Q=current I×time T. In other words, the current I is inversely proportional to the time I when the capacity remains unchanged. Thus, when the charging current is increased, the battery will soon be fully charged, this is so-called speedy charger. But, by use this method, the power of inside exchange power source is considerably demanded, and the size of the coils in the transformer must be increased. As shown in FIG. 3, the exchange power source of this kind of a speedy charger 20 connects outside and forms an AC/DC transformer 21. The plug 22 or the plug 23 with extending cable connects to the power source. This charger is not convenient to take and its production cost will be raised.
We can conclude from the description above, that instant charger and speedy charger has also its advantages and defects. How the practical function of speedy charger as well as the low power and the small size of instant charger can be combined, is the subject which will be solved in the invention.